The present invention relates to a thermosensitive image transfer medium which is capable of yielding images with high image density by a small amount of thermal energy consumption, and uniform image density even if image transfer is done multiple times from the same thermosensitive image transfer medium, and the thus obtained images are improved on the light resistance and heat resistance.
Conventionally, there are known several thermosensitive image transfer mediums. For example, a thermosensitive image transfer medium consisting of (i) an image transfer sheet comprising a thermal-sublimation-type dye layer formed on a support material and (ii) an acceptor sheet capable of accepting the sublimated dye images from the thermal-sublimation-type dye layer of the image transfer sheet when thermal printing is performed from the back side of the image transfer sheet.
Another conventional thermosensitive image transfer medium consists of (i) an image transfer sheet comprising an image transfer layer formed on a support material, which image transfer layer comprises a thermo-fusible material and a pigment or a dye, and (ii) an acceptor sheet.
The former thermosensitive image transfer material has the shortcomings that the dye images on the acceptor sheet are poor in preservability because of the use of the thermal-sublimation-type dye and, therefore, an overcoating must be provided on the transferred images.
In the latter thermosensitive image transfer medium, the image transfer layer contains a pigment or a dye dispersed in the thermo-fusible material. In this thermosensitive image transfer medium, if a large quantity of the pigment is contained in the image transfer layer in an attempt of obtaining images with high density, the image transfer efficiency decreases, and the result is that it becomes difficult to obtain images with high density, and if a large quantity of the thermo-fusible material is contained in the image transfer layer in order to increase the thermosensitivity, a large quantity of the thermo-fusible material is transferred from the transfer sheet to the acceptor sheet in the course of image transfer and, as a result, it becomes difficult to smoothly peel the transfer sheet off the acceptor sheet and line images on the acceptor sheet become unclear.
In addition to the above-described conventional thermosensitive image transfer mediums, a further thermal printing type thermosensitive image transfer medium is known, in which materials which react with each other to form a color upon application of heat thereto are supported separately in the form of two layers, each layer on a different support material, and thermal printing is performed by bringing the two layers into close contact with each other. In thermosensitive image transfer mediums of this type, the coloring reaction does not occur sufficiently if the image transfer layer is merely transferred to the acceptor layer by bringing them into contact with each other, thus yielding images with low image density. If thermal printing were performed at high temperatures, with application of heat for a long period of time for allowing the coloring reaction to take place sufficiently, images with high density would be obtained on the acceptor sheet. However, the coloring reaction would also take place on the image transfer sheet at the same time. In other words, image formation occurs on both the acceptor sheet and the image transfer sheet.
The inventors of the present application have proposed in Japanese Laid-open Patent Application Ser. No. 57-139347 a thermosensitive image transfer medium, whose acceptor sheet has an acceptor layer containing a porous filler with relatively great oil absorption capability, thereby making improvement on the above described conventional shortcomings.
By this thermosensitive image transfer medium, images with comparatively high image density can be obtained even if it is used a number of times for multiple image transfer. However, the light resistance, the heat resistance and the image density of the images were not satisfactory.